Vaisala RVP900

USER’S MANUAL__________________________________________________________________
192 _________________________________________________________________ M211322EN-D
where:
If the three pulse powers have the property that:
(Alg.1
5
)
then (I
n
, Q
n
) is replaced by (I
n-1
, Q
n-1
). Here C
1
and C
2
are constants that
can be tuned by the user to match the type of interference that is
anticipated, and the error rates that can be tolerated. For certain
environments it may be the case that good results can be obtained with C
1
= C
2
; but the RVP900 does not force that restriction.
This 3-pulse algorithm is only intended to remove interference that arrives
on isolated pulses, and for which there are at least two clear pulses in
between. Interference that tends to arrive in bursts will not be rejected.
Two variations on the fundamental algorithm are also defined. The
CFGINTF command (Section 7.23 Configure Interference Filter
(CFGINTF) on page 324) allows you to choose which of these algorithms
to use, and to tune the two threshold constants. You may also do this
directly from the Mp setup menu (Section 4.2.2 Mp — Processing Options
on page 106).
(Alg. 2)
(Alg. 3)
Where LinAvg() denotes the deciBel value of the linear average of the two
deciBel powers. The Alg.2 and Alg.3 algorithms also include the receiver
noise level(s) as part of their decision criteria. Whenever power levels are
intercompared in the algorithms, any power that is less than the noise level
is first set equal to that noise level. This makes the filters much more robust
and properly tunable, so that interference is more successfully rejected on
top of blank receiver noise.
Optimum values for C
1
and C
2
will vary from site to site, but some
guidance can be obtained using numerical simulations. The results shown
P
n
10log
10
I
2
n
Q
2
n
+=
P
n 1–
P
n 2–
– C
1
and P
n
P
n 1–
– C
2

P
n 1–
P
n 2–
– C
1
and P
n
P
n 1–
– C
2

P
n 1–
P
n 2–
– C
1
and P
n
LinAvg P
n 1–
,P
n 2–
– C
2
